The present invention relates to bicycle frames and more particularly to a bicycle frame that maximizes energy efficiency and provides a smooth ride by incorporating improved vertical flexibility and increased lateral stiffness in the structure of the frame.
Conventional bike frames are substantially rigid, making them uncomfortable to ride under some circumstances, particularly over rough terrain. To overcome this problem, a number of bikes have incorporated springs and shock absorbers in the frame structure. Springs and shock absorbers increase vertical cushioning in the frame but they add extra components, complexity, and weight to the frame structure and tend to decrease the responsiveness of the frame. In particular, they tend to decrease the lateral or torsional rigidity of the frame, which is undesirable.
A number of bikes have been developed wherein flexibility has been incorporated into the frame itself. In a bike frame previously developed by the present inventor, a steel cable replaces the conventional down tube in the bike frame, and a leaf-type spring is incorporated in the top tube of the frame. The cable is connected to a coil spring that effectively permits elongation of the cable. Other bike frames have incorporated flexibility by other means, including the incorporation of leaf springs in the frame at different locations.
A problem with some prior frames is that the incorporation of too much flexibility in the frame can cause the frame to absorb and dissipate pedaling energy input and produce energy loss. Thus, it sometimes takes more energy to pedal a bike that incorporates energy absorption characteristics than it does to pedal a bike having a more rigid frame. Also, when resilience is desired, different amounts of resilience are desired for different types of bicycles and different types and sizes of riders. Bicycles usually are not adjustable to accommodate these differences.
Where the energy efficiency of a bike frame is of principal importance (such as a road bike), conventional thinking has been that efficiency is maximized by maximizing frame stiffness. In the present invention, this has been found not to be the case. The vertically flexible frame of the present invention appears to increase energy efficiency as well as improve the smoothness of the ride. A too stiff frame produces a harsh ride.
An object of the present invention is to provide an improved bike frame that has sufficient vertical flex to provide a smooth ride and absorb shocks and yet limits lateral or torsional flex and maximizes energy responsiveness of the frame. Another object of the present invention is to provide a bicycle frame wherein the resilience and riding characteristics can be adjusted or modified for different riders and different riding conditions by the use of different interchangeable frame components.
These and other features and advantages of the present invention will hereinafter appear and for purposes of illustration but not of limitation a preferred embodiment of the invention is described and shown in the appended drawings.